Electron beam addressed plasma display panel

ABSTRACT

A combination display and storage tube of the type having gasfilled cells sandwiched between flat insulating sheets. One of the two electrodes for applying the sustaining voltage to the gas-filled cells is provided with apertures so that an electron beam may be used to initiate or extinguish the discharge of selected cells.

United; States Patent.

Robert 0. Gregory St. Louis, Mo. 808,1 95

Mar. 18, 1969 May 18, 1971 Monsanto Company St. Louis, Mo.

Inventor Appl. No. Filed Patented Assignee ELECTRON BEAM ADDRESSEDPLASMA DISPLAY PANEL 8 Claims, 7 Drawing Figs.

11.5. C1 313/89, l78/7.5D, 313/108B, 313/329, 315/169TV Int. Cl H01 j29/10, H05b 33/02 Field of Search 313/108,

[56] References Cited UNITED STATES PATENTS 2,500,929 3/1950 Chilowsky313/109X 2,972,707 2/1961 Wood 315/362 3,262,010 7/1966 Kazan 315/633,334,269 8/1967 LHeureux 313/89X 3,499,167 3/1970 Baker et a1 315/1693,509,421 4/1970 Holz 3 l 5/169X Primary ExaminerRoy Lake AssistantExaminer-E. R. La Roche Attorneys-John D. Upham, Herman O. Bauermeisterand Harold R. Patton ABSTRACT: A combination display and storage tube ofthe type having gas-tilled cells sandwiched between flat insulatingsheets. One of the two electrodes for applying the sustaining voltage tothe gas-filled cells is provided with apertures so that an electron beammay be used to initiate or extinguish the discharge of selected cells.

Patented May 18, 1971 3,579,015

Cvons) FIG.6

| CvoLTs) l I l INVENTOR C ROBERT GREGORY ATTORNEY ELECTRON BEAMADDRESSED PLASMA DISPLAY PANEL FIELD OF THE INVENTION The presentinvention relates generally to an information storage and/or displaytube of the plasma or gas discharge type, and more particularly, to astorage tube having lightemitting elements which may be turned on andoff by means of an electron beam.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART In thefield dealing with the storage and display of information, it has beensuggested that plasma display panels be employed to take advantage oftheir inherent memory; i.e. bistable mode of operation, long life andhigh brightness. See for example, proceedings, Fall Joint ComputerConference The Plasma Display-A Digitally Addressable Display WithInherent memory, by D. L. Bitzer and H. G. Slottow, Nov. i966, p. 541,Such plasma display panels generally comprise three laminated sheets offlat glass plates. The center glass laminate being provided with anarray of small gas-filled apertures, referred to as bistable plasmadisplay cells. A visual gas discharge may be achieved by properselection of the gas mixture and the application of a voltage signal ofan appropriate value to selected cells.

The discharge of each cell can be made independent of all other cellsand is bistable in nature. That is, a sustaining AC voltage having avalue less than the critical firing voltage may be applied across allcells, and although it is sufficient to sustain half-cycle dischargesonce initiated, it effects no discharge until it is combined with anactuation voltage to render the total cell voltage greater than thecritical firing voltage. Once the half-cycle discharge is initiated, theinformation signal may be removed, yet the cell will continue to emitlight under the influence of the sustaining field. Thus, bistableoperation is achieved.

I-leretofore, the outer laminates of plasma display panels of the typejust described have been provided with a crossed-grid arrangement ofelectrical conductive strips for the purpose of applying the "sustainingand actuation voltages to the cells selected for discharge operation.Application of an actuation voltage pulse to two crossed-grid conductorsresults in the energization or discharge of the gas-filled cell providedat the intersection of the two conductive strips,

The crossed-grid conductor arrangement for addressing the light-emittingcells of plasma display panels has been employed satisfactorily incertain applications. However, the deposition of conductive strips is atime-consuming and an expensive step in the manufacture of paneldisplays embodying a large number of cells for high resolution.Furthermore, elaborate switching circuitry capable of handling voltagesof several hundred volts, is required to properly select the properconductive strips required to store or display the information.

SUMMARY OF THE INVENTION The general purpose of this invention is toprovide a storage tube of the plasma display type, which embraces all ofthe ad vantages of similar plasma display panels yet does not possessthe aforedescribed disadvantages. To attain this, the present inventionutilizes an electron beam addressing arrangement for energizing anddeenergizing selected plasma display cells.

An object of the present invention is the provision of aplasma-display-type direct view storage tube, the manufacture of whichis susceptible to relatively simple production techniques.

Another object of the present invention is the provision of a directview storage tube, wherein information can be selec tively stored orerased at electron beam scanning speeds.

In the present invention these purposes (as well as others apparentherein) are achieved generally by a storage tube having substantiallyflat insulating members separated by a plurality of plasma dischargecells. The cells are filled with an ionizable gas or gas mixture andelectrodes are secured to the outer surfaces of the insulating members.One of the electrodes is continuous and transparent, while the other isa thin conductive metal layer having apertures arranged over gasfilledcells. An AC power supply is connected between the two electrodes toprovide a sustaining potential. An electron beam addressing system isemployed to direct an electron beam through the apertures of the metalelectrode to energize and deenergize selected cells.

BRIEF DESCRIPTION OF THE DRAWINGS Utilization of the present inventionwill become apparent to those skilled in the art from the disclosuresmade in the following description, as illustrated in the accompanyingdrawings; in which FIG. 1 is a perspective view of a storage tubeconstructed in accordance with the present invention;

FIG. 2 is an enlarged broken-away, cross-sectional view of a displaypanel portion of the storage tube of FIG. 1;

FIG. 3 is an enlarged, detailed view revealing a portion of one of theelectrodes deposited on the display panel portion of FIG. 2;

FIG. 4 is a schematic view of the electron beam addressing system andcircuit connections of the storage tube of FIG. 1;

FIG. 5 is a schematic representation of wall charge accumulation duringa portion of the operation of the storage tube of FIG. l;'and

FIG. 6 is a graphical representation of waveforms corresponding to thewall charges and applied voltages when the cell in in the on state,employed to store and display information by means of the storage tubeof FIG. 1.

THE INVENTION Referring now to the drawing, wherein like referencecharacters designate like or corresponding parts throughout the severalviews, there is shown in FIG. 1 a storage tube, designated 10. Thestorage tube 10 consists generally of a gas discharge or plasma displaypanel 12 having a viewing surface 14, an evacuated glass envelope 16sealed to and extending from the panel 12, and an electron beamaddressing system 18. The evacuated glass envelope 16 is sealed to theplasma display panel 12 and encloses the electron panel addressingsystem 18. It may be constructed in accordance with wellknown cathoderay tube fabrication techniques.

Referring to FIG. 2, it may be seen that the plasma display panel of thepresent invention consists of three fiat sheets of insulating material,such as glass. A center sheet 20 is sandwiched between two outerlaminates 22 and 24, and has a plurality of apertures or cells 26 formedthrough it, by drilling, etching or other means. The density of thecells 26 determines, in part, the resolution of the panel 12. In myexperiments, I have used glass sheets 0.006 inch in thickness with adistance between adjacent cells of 0.025 inch, thereby providing a celldensity of approximately 1,600 cells per square inch.

The cells 26 are charged with a suitable gas or gas mixture; forexample, a mixture of percent neon and 5 percent nitrogen at a pressureof 300 Torr has been found to provide an extremely fast, brightdischarge.

The outer surface of the glass sheet 22 is covered by a continuous,transparent electrode 28 such as stannous oxide, SnO while the outersurface of the outer laminant 24 is provided with a conductive-metalelectrode 30, such as an aluminum film layer. The electrode 30 isprovided with apertures or openings 32 arranged in registration with thegas-filled cells 26, as may best be seen in FIG. 3.

Referring now to FIG. 4, the electron beam addressing system 18 of thepresent invention is shown in schematic form, the evacuated envelope,mounting elements, and external terminals being omitted for purposes ofclarity. The electron gun structure 34 consists of a suitably groundedcathode electrode 36, heated by a filament 38. An accelerating potentialrepresented by a battery 40 is connected between the cathode 36 of theelectron gun and the electrode 30 of the gas discharge panel 12.Alternatively, the apertured electrode, 30, may be operated at groundpotential with the cathode at a high negative potential. By way ofexample, the electron gun structure 34 may be an electron guncommercially available from Superior Electronics Company and referred toas a SAQP electron gun, and the accelerating potential may be 6.5 kv.

It should be apparent that electrons emitted from the cathode 36 of theelectron gun structure 34 are caused to be accelerated by theaccelerating potential 40 along a path toward the apertured electrode 30of the panel display 12. Between the panel display 12 and the electrongun assembly 34, there are provided horizontal and vertical deflectionplates 42 and 44, between which the electron beam passes and to whichappropriate deflection circuitry (not shown) may be externally connectedfor the purpose of directing the electron beam to selected apertures 32.A beam-gating grid 46 is disposed between the horizontal deflectionplates 42 and the electron gun assembly 34 and is connected tobeam-gating input terminal, as indicated at 48. The beam-gating inputterminals 48 may be connected to an appropriate input signal sourcesynchronized with the external deflection circuitry in accordance withwell-known techniques. Thus, it is possible to modulate the intensity ofthe electron beam emanating from the electron gun assembly 34 during thescanning or sweeping of the beam across the display panel 12.

As may be seen in FIG. 4, an AC voltage source 50 is connected betweenthe electrodes 28 and 30 of the gas discharge panel 12. The AC signalsource 50 may be chosen to provide to the electrodes 28 and 30 a 500volt peak sustaining voltage at a frequency of 300 kHz.

In operation, the AC voltage source 50 is applied to the electrodes 28and 30 of the plasma display panel 12 to provide the necessarysustaining potential. In the absence of any additional potential acrossthe cells, the sustaining voltage is insufficient to develop thecritical firing voltage V, required to initiate plasma discharge of thegas within the cells 26.

Information can be written" on or stored within the storage tube 10 byapplying an input signal to the beam-gating input terminal 48 so thatthe beam-gating grid 46 allows electrons to be accelerated from theelectron gun cathode 36. These electrons are then deflected by thehorizontal and vertical deflection plates 42 and 44; the amount ofhorizontal and vertical deflection corresponding to deflectionpotentials applied thereto. The deflection signals may be synchronizedwith the application of the input signal in any well-known fashion sothat selected cells are properly energized.

The deflection plates direct the accelerated electrons to the selectedaperture of the aluminum electrode 30, where they accumulate on thesurface of the glass sheet laminate 24. This electron accumulationresults in an electrical charge, and therefore electrical field, acrossthe gas-filled cells arranged in registration with the aperture to whichthe electrons have been directed. The electrical field so establishedwill aid the field resulting from the sustaining voltage during one-halfcycle. Although the initial potential across the gas-filled cells isinsufficient to produce plasma discharge, the additional potentialprovided by the accumulation of electrons at the aperture surface ofglass sheet 24 will trigger the selected cell to its on state.Subsequently, the electron beam may be turned off by the beam-gatinggrid 46 of the electron beam structure 34, yet the energized cell willremain in its on state. For the cell to be later extinguished, oncommand, requires that the charge deposited on the dielectric surface bythe electron beam be dissipated after having triggered the cell into the"on" state. I have observed that in the range of vacuum normally usedfor high-vacuum tubes (l torr) that the charge dissipates inapproximately IO seconds. This is due to positive ion bombardment fromthe residual gas in the vacuum and surface leakage. By proper surfacetreatment, such as application of a thin, high resistivity, layer ofstannous oxide to the surface; the decay of electron beam depositedcharge can be made as rapid as desired.

The electron beam can then be repositioned by means of the horizontaland vertical deflection plates 42 and 44 to energize another gas-filledcell in a like manner. The sustaining voltage provided by the AC voltagesource 50 serves to maintain the plasma discharge of those cells whichare triggered on by means of the electron beam, even after the electronbeam has been turned off or removed.

Thus, it may be seen that information, such as alphanumeric characters,may be written on the plasma display panel 12, where it may be storedindefinitely. The plasma discharge provides a bright visual display ofthe information, When it becomes desirable to erase an entire characteror all of the information displayed by the storage tube 10, the ACvoltage source 50 may be turned off, thereby reducing the potentialacross the actuated cells to a level insufficient to maintain the plasmadischarge.

The storage characteristic of a plasma display panel arises from thewall charge generated in each cell 26 as free charges during the gasdischarge. These wall charges tend to migrate to the cell walls underthe influence of the sustaining AC potential, and therefore arrangethemselves so as to aid or add to the applied AC field at the beginningof each half-cycle of the applied AC sustaining voltage. These wallcharges are represented in FIG. 5 for a single gas-filled, energizedcell. Waveform representation of the applied AC sustaining voltage isshown in FIG. 6a, while a similar representation of the wall chargepotential is shown in FIG. 6b.

Referring specifically to the time interval indicated between the time1,, and time t, in FIG. 6, it may be seen at time I, the combinedelectrical field resulting from the wall charge and that of the ACsustaining voltage signal is sufficient to fire or discharge the cell.As may be seen, the discharge of the cell reverses its wall chargepolarity very rapidly so that the next half-cycle of operation repeatsthe discharge'phenomenon.

However, I have found that during the time interval between time t and tthe electron beam may be pulsed to erase or deenergize a cell which isin its on state. The pulsed electron beam deposits a charge on thedielectric surface upon which it impinges after passing through aselected aperture of the aluminum electrode 30. The deposited chargeopposes the electric field of the wall charge during the time periodbetween time t and time t,. Therefore, if the deposited charge issufficiently large and if it is applied between time t and 1,, the totalelectrical field across the cell will be insufficient to sustain thedischarge which would otherwise occur at time 1,, resulting in the cellreverting to its off condition during the next half-cycle of the ACsustaining voltage signal. If the decay of the charge deposited by theelectron beam is not too 7 fast relative to the decay of the wallcharge, the cell will remain off for all subsequent half-cycles ofoperation, or until again energized by the electron beam. Hence, anenergized cell may be efficiently extinguished in accordance with myinvention.

In summary, the storage tube of the present invention employs a uniqueelectron beam addressing system directly applied to the dielectricsurface material of a plasma-displaytype panel in registration withcells to be triggered on or off. Such a storage tube may beadvantageously used as a storage oscilloscope where it is important thatthere by no loss of resolution of a displayed signal trace with thepassage of time. Another application of my storage tube would be that ofa data display or storage memory; for example, in computer time-sharingscientific and educational applications. In these latter applicationsthe resolution, indefinite storage time and selective erasure, presentadvantages not available with other types of data display system.

Many modifications and variations of the present invention are possiblein view of the above teachings. Therefore, it is to be understood thatthe invention may be practiced otherwise than as specifically described.

I claim:

l. A storage tube Comprising a plurality of substantially flatinsulating members defining storage cells therebetween,

an ioniz'able gas within and filling said storage cells,

a pair of electrodes external to and separated from said cells by saidinsulating members, one of said electrodes defining apertures registeredwith said gas-filled cells,

power supply means connected to said electrodes for providing asustaining potential less than that required to initiate a plasmadischarge of said gas-filled cells but sufficient to sustain suchdischarge once initiated,

electron beam addressing means positioned to direct an electron beamthrough selective apertures of said one electrode and onto the surfaceof one of said insulating 'members,

whereby electrical charges may be applied to said gas-filled cells toselectively initiate discharge or terminate discharge of the gasprovided therein.

2. The storage tube, as defined in claim I, wherein said power'supplymeans is an AC voltage source.

3. A storage tube, as defined in claim 1, wherein the other of saidelectrodes is a continuous transparent material.

4. The storage tube, as defined in claim 1, wherein said one electrodehaving apertures therein is a substantially continuous thin-filmconducting layer.

5. The storage tube, as defined in claim 1, wherein said electron beamaddressing means, comprises an electron gun,

a DC potential source connected between said gun and said one electrodeto accelerate electrons emitted by said gun,

deflection plates positioned between said electron gun and said oneelectrode for directing electrons emitted by said gun to selectedapertures provided in said one electrode, and

an electron beam-gating grid positioned between said deflection meansand said electron gun for gating the emission of electrons from said gunin response to electrical signals applied to said grid.

6. A combination display and storage tube, comprising an evacuatedenvelope housing an electron gun, deflection plates, and an electronbeam-gating grid,

a face plate including a panellikestructure of an insulating materialand having a plurality of gas-filled cavities formed therein, thegas-filled cavities being charged with an ionizable gas,

a pair of electrodes external to and separated from said gas filledcells by said insulating material, one of said electrodes definingapertures registered with said gas-filled cells, the other electrodebeing a continuous transparent electrode,

an AC power supply means connected between said electrodes for providinga sustaining potential less than that required to initiate discharge ofsaid gas-filled cells, but sufficient to sustain such discharge onceinitiated,

means for controlling an electron beam emitted by said electron gun,whereby said electron beam may be selectively applied to said gas-filledcells through said apertures of said one electrode to initiate andextinguish the plasma discharge of gas provided therein.

7. A method of addressing a storage tube of the type having a plasmadisplay panel comprising a plurality of gas-filled, light-emitting cellsformed within an insulating material, comprising the steps of I applyingto said gas-filled cells by means of electrodes external thereto an ACvoltage signal having a magnitude insufficient to initiate discharge ofthe gas therein, but sufficient to sustain the light-emitting dischargeonce initiated, and

directing an electron beam onto the surface of said insulating materialin registration with selected gas-filled cells, said electron beamhaving an intensity sufficient in combination with said AC voltagesignal to trigger the individual disglae cells to theirplasma dischar estate. 8. The metho o returning individual gas-fille cells formed withininsulating material of a plasma display storage panel to their initialnonlight-emitting states, comprising the steps of directing an electronbeam to the surface of said insulating material in registration withcells to be returned to their off state, and pulsing an electron beamduring an appropriate half-cycle time interval to deposit a charge onsaid surface in op- 7 position to wall charges developed within saidcells.

1. A storage tube comprising a plurality of substantially flatinsulating members defining storage cells therebetween, an ionizable gaswithin and filling said storage cells, a pair of electrodes external toand separated from said cells by said insulating members, one of saidelectrodes defining apertures registered with said gas-filled cells,power supply means connected to said electrodes for providing asustaining potential less than that required to initiate a plasmadischarge of said gas-filled cells but sufficient to sustain suchdischarge once initiated, electron beam addressing means positioned todirect an electron beam through selective apertures of said oneelectrode and onto the surface of one of said insulating members,whereby electrical charges may be applied to said gas-filled cells toselectively initiate discharge or terminate discharge of the gasprovided therein.
 2. The storage tube, as defined in claim 1, whereinsaid power supply means is an AC voltage source.
 3. A storage tube, asdefined in claim 1, wherein the other of said electrodes is a continuoustransparent material.
 4. The storage tube, as defined in claim 1,wherein said one electrode having apertures therein is a substantiallycontinuous thin-film conducting layer.
 5. The storage tube, as definedin claim 1, wherein said electron beam addressing means, comprises anelectron gun, a DC potential source connected between said gun and saidone electrode to accelerate electrons emitted by said gun, deflectionplates positioned between said electron gun and said one electrode fordirecting electrons emitted by said gun to selected apertures providedin said one electrode, and an electron beam-gating grid positionedbetween said deflection means and said electron gun for gating theemission of electrons from said gun in response to electrical signalsapplied to said grid.
 6. A combination display and storage tube,comprising an evacuated envelope housing an electron gun, deflectionplates, and an electron beam-gating grid, a face plate including apanellike structure of an insulating material and having a plurality ofgas-filled cavities formed therein, the gas-Filled cavities beingcharged with an ionizable gas, a pair of electrodes external to andseparated from said gas-filled cells by said insulating material, one ofsaid electrodes defining apertures registered with said gas-filledcells, the other electrode being a continuous transparent electrode, anAC power supply means connected between said electrodes for providing asustaining potential less than that required to initiate discharge ofsaid gas-filled cells, but sufficient to sustain such discharge onceinitiated, means for controlling an electron beam emitted by saidelectron gun, whereby said electron beam may be selectively applied tosaid gas-filled cells through said apertures of said one electrode toinitiate and extinguish the plasma discharge of gas provided therein. 7.A method of addressing a storage tube of the type having a plasmadisplay panel comprising a plurality of gas-filled, light-emitting cellsformed within an insulating material, comprising the steps of applyingto said gas-filled cells by means of electrodes external thereto an ACvoltage signal having a magnitude insufficient to initiate discharge ofthe gas therein, but sufficient to sustain the light-emitting dischargeonce initiated, and directing an electron beam onto the surface of saidinsulating material in registration with selected gas-filled cells, saidelectron beam having an intensity sufficient in combination with said ACvoltage signal to trigger the individual display cells to their plasmadischarge state.
 8. The method of returning individual gas-filled cellsformed within insulating material of a plasma display storage panel totheir initial nonlight-emitting states, comprising the steps ofdirecting an electron beam to the surface of said insulating material inregistration with cells to be returned to their ''''off'''' state, andpulsing an electron beam during an appropriate half-cycle time intervalto deposit a charge on said surface in opposition to wall chargesdeveloped within said cells.